One uses actually for the reprofiling of the rails, machines comprising controlled grinding units as disclosed in patents CH 606.616 or CH 633.336; These devices present the drawback that one must reposition the grinding wheel against the rail at each angular adjustment of the angle of the grinding wheel. Furthermore, the angular amplitude of the pivoting of the grinding units is limited.
The patent GB-A-1.151.010 also discloses a device for reprofiling the rail head of at least one rail, comprising a support carrying at least one grinding unit, presenting at least one grinding wheel driven in rotation by a motor and means of axial displacement of that grinding wheel to apply it against a side line of the head of the rail thus compensating its wearing off.
A well known problem for the rail reprofiling machines is that one must be able to grind the inside side, the running table and the outside side of the rail with the same grinding wheel. This is especially imperative when preparing the rails for their mutual replacement. With existing machines, this can only be achieved with time consuming manual regulation and bulky grinding units, because their axial stroke, parallel to the rotation axis of the grinding wheel are necessarily important, finally these great axial strokes affect the precision of the grinding.
The EP 0 145 919 patent discloses a machine having one or more grinding wheel which can pivot on a large angle, namely, about 180.degree., which is a much greater angle than on existing machines, thus avoiding conflict, during the grinding wheel's rotation, between the grinding wheel and other object such as fish plate or coach screw present along the railway track. Furthermore, to insure a high quality of grinding, one must avoid a change in the grinding wheel position which implies an important correction of its axial position, parallel to its rotation axis, in order to bring it back in contact with the rail.
In all these embodiments, the grinding units are mounted on trolleys or underframes suspended under a railroad vehicle and resting on one of the rails by means of a guide roller. Therefore, the grinding reference plane is defined by the rolling surface of the rail which is worked on, and not by the plane of the track. Once the rail is badly worn, the running table plane is modified in such a way that the reprofiling of the rail is carried out on the basis of an imprecise reference plane. Moreover, due to the use of pivoting grinding units comprising a motor which drives two grinding wheels in rotation, the height of these units requires an important available space under the railroad vehicle, and therefore becomes difficult to locate guide carriages under it.
The reprofiling device disclosed in the patent CH 675.440 remedies this drawback by mounting the grinding units on the framing of a railroad vehicle which comprises a two-wheel axle at one of its extremity and which is articulated around an axis parallel to the longitudinal axis of the railway at its other extremity on a rigid frame having two wheels. Thus, the framing is guided by the railway track and defines a reference plane parallel to the plane of the railway track.
All the previously reviewed devices use grinding wheels having a planar working surface which leaves, after the grinding process, longitudinal facets on the head of the rail. Furthermore, the use of lapidary grinding wheels give rise to scratches transversal to the rail. When grinding with high power, these facets and scratches may be important and influence negatively the fatigue strength of the rail.
One still knows other reprofiling devices disclosed in the patents DE-26 12 174 and DE-26 12 173 in which grinding units are pivotally mounted on a frame, which is mounted in such a way that it can move vertically with regards to a trolley rolling on the railway track. This trolley is laterally extensible and comprises means leading to spread it so that its flanged wheels are always applied against the inner side of the rail in order to guide the trolley along the railway track. This device comprises, unlike the preceeding one, shaped grinding wheel reprofiling a relatively important length of the perimeter of the head rail's profile and not only a rectilinear small facet of it. On the other hand, these devices are not satisfactory especially in a curve; the reason being that, the length of the trolley being important because it has to carry several grinding units, the guiding of the grinding wheels with regards to the rail is not precise enough an may provoke either the rupture of the grinding wheels or an inadequate and very inacurate reprofiling of the rail.
Furthermore in a warped curve, the supporting strength of the guide roller against the outer rail should be large enough to compensate the retaining strength of the grinding wheel on the one hand and the component of the weight of the trolley on the other hand.
For the inner rail, the supporting strength will be equal and opposite to the one acting on the outer rail added with the component of the trolley's weight, and thus, this supporting strength is very high.
In a curve, due to the relatively great length between the wheels of the trolley (2 meters or more), the deflection between the contact line of the wheels and the support point of the most centered grinding wheel is important (about 5 mm for a curve radius of 100 m.) and for the inner rail of the curve this grinding wheel must support the above-mentioned supporting strength; it generally leads to the rupture of one or several grinding wheels.
In the small radius curve, having a radius between 100 m. and 250 m., the rails are laid with a gauge clearance between 15 mm to 35 mm depending on the railway network and the rolling vehicles.
When grinding rails in those curves use grinding units carried by trolleys which are guided by the rails, the grinding wheel axis is shifted from a value equal to the deflection between the roller of the trolley augmented with the gauge clearance of the railway. This important shift of the grinding wheel's axis provokes a lowering of the inferior grind-stone's axis which may be as important as 50 mm or more for a 45.degree. inclined grinding wheel. This is not acceptable because the grinding wheel interferes notably with the rail fastening which leads to rupture of the grinding wheels.
The device disclosed in the DE-26 12 174 patent, which is relatively simple allows to compensate the gauge clearance of the railway in a small radius curve, but not the deflection of the trolley which is large enough to induce the grinding wheel's rupture as seen before.
Document EP-A-0344390 still discloses a trolley presenting a roller intermediate to the grinding units in order to adjust their orientation and their position with regards to the rail. One should note that the disclosed device works only with a peripheral grinding wheel which induces other drawbacks.
Furthermore, in the devices disclosed in both document DE-26 12 174, and EP-A-0344 390 the tranversally extensible trolleys should apply a very high spacing strength against the flange wheels to compensate in inclination the components of the total weight of the trolley as well as the weight of the grinding units and the grinding supporting force. Because of this important spacing force, the derailment of the trolleys are frequent, especially when the rails present a bevelling wear.